(a) Field of the Invention
The present invention relates to a coupled torsion beam axle type suspension system, and more particularly, to a coupled torsion beam axle type suspension system that improves single impact characteristics of an outer rear wheel with respect to thrust and drag forces as well as controlling movement (i.e., toe) characteristics thereof with respect to a side force, when a vehicle turns.
(b) Description of the Related Art
Generally, despite limitations in design performance factors such as ride comfort, driving stability, etc., a coupled torsion beam axle type suspension system (hereinafter referred to as a CTBA) has been primarily applied to rear wheel suspension systems for compact and mid-size cars. These CTBA systems are used instead of independent-type suspension systems, because they are advantageously light weight and low cost to make due to their simplified components.
FIG. 1 is a perspective view of a CTBA according to one example of the related art. Referring to FIG. 1, the exemplary CTBA according to the related art is provided with a torsion beam 1 in a width direction of a vehicle, trailing arms 5 respectively coupled to opposite ends of the torsion beam 1, and carriers 3 for mounting wheel tires at the trailing arms 5. A spring seat 9 for mounting a spring 7 thereon and a shock absorber pin 13 for coupling with a shock absorber 11 are also provided at a rear inner portion of the trailing arm 5. In addition, a vehicle body-engaging unit 15 is provided at a front end portion of the trailing arm 5 to be coupled to a vehicle body.
More specifically, each vehicle body-engaging unit 15 includes a trailing arm bushing 21 that is coupled to the front end portion of the trailing arm 5, and a mounting bracket 23 that is coupled to the trailing arm bushing 21 through a bolt 25.
CTBAs that have the aforementioned configuration, often result in wheel deformation due to the twisting deformation characteristics of the torsion beam 1. The positions of the trailing arm 5 and the configuration of the vehicle body-engaging unit 15 may also cause deformation of the wheels.
Vehicles should maintain a certain level of under-steering tendency to stabilize the vehicle during turns. For this purpose, ideally a rear outer wheel of the vehicle while making a turn (hereinafter referred to as a rear outer wheel) should be induced to toe-in and a rear inner wheel of the vehicle while making a turn (hereinafter referred to as a rear inner wheel) should be induced to toe-out.
However, this type of conventional CTBA has certain problems in performing this movement. For example, FIG. 2 is a top plan view illustrating movement characteristics of the coupled torsion beam axle type suspension system, applied with a side force, according to one example of the related art.
As shown in FIG. 2, though the CTBA according to one example of the related art is not mechanically moveable when applied with a side force F1, the entire CTBA rotates due to the deformation of the trailing arm bushing 21 and generates a toe angle at the rear outer wheel W1.
That is, when the vehicle makes a turn, the rear outer wheel W1 is applied with the side force F1 and thus is likely to be induced to toe-out, while the rebounded rear inner wheel W2 is applied with the side force F1 and thus is likely to maintain the previous toe angle or to be induced to toe-in. This results in the vehicle being over-steered in general, thus reducing the stability of the vehicle.
As a mechanical instantaneous rotational center point SP of the CTBA with respect to the vehicle body (i.e., an intersection of lines that extend in engaging directions of the trailing arm bushings 21 engaged to the vehicle body) is positioned in front of the wheel centers WC, the rear outer wheel W1 has a tendency to toe-out due to the side force F1 while the rear inner wheel W2 has a tendency to toe-in due to the side force F1.
In order to solve such a turning stability problem in the conventional CTBA, suspension systems are currently being developed to improve a structure of the vehicle body and the vehicle body-engaging unit of the trailing arm 5 so that the instantaneous rotational center point SP of the CTBA with respect to the vehicle body is positioned behind the wheel centers WC.
FIG. 3 is a top plan view of a coupled torsion beam axle type suspension system according to another example of the related art. Referring to FIG. 3 the improved CTBA according to the another example is provided with a rotation link 31 as a vehicle body-engaging unit 15 between a vehicle body and a trailing arm bushing 21, such that an instantaneous rotational center point SP with respect to the vehicle body is positioned behind wheel centers WC.
That is, a rear end portion of the rotation link 31 is engaged in parallel to the trailing arm bushing 21 in a width direction of the vehicle, and a front end portion thereof is provided with a vehicle body-mounting bushing 33 that is moveable with respect to the vehicle body in a rotational direction, thereby being engaged to one lower portion of the vehicle body.
In this case, the vehicle body-mounting bushing 33 is coupled to the trailing arm bushing 21 through the rotation link 31 and is engaged to the vehicle body in the height direction of the vehicle, such that it is engaged to the vehicle body at an outer front of the rotation link in the width direction of the vehicle. Thus, the instantaneous rotational center point SP of the CTBA with respect to the vehicle body is formed at an intersection of the extending lines that connect centers S1 of the mounting bushings 33 with centers S2 of the trailing arm bushings 21, and is positioned behind the wheel centers WC.
As such, in this CTBA, the instantaneous rotational center point SP with respect to the vehicle body is positioned behind the wheel centers WC, so that it has certain movement characteristics with respect to the side force F1 and the thrust and drag forces that are described below with reference to FIGS. 4A-C.
FIGS. 4A-C are top plan views illustrating movement characteristics of the coupled torsion beam axle type suspension system, applied with the side force and the thrust and drag forces, according to another example of the related art. In FIG. 4 A, when rear wheels are applied with the side force F1, the rear outer wheel is induced to toe-in while the rebounded rear outer turning wheel W2 maintains a set toe-in angle or is induced to toe-out, such that the vehicle is generally under-steered to secure the turning stability. Meanwhile, the CTBA is induced to rotate based on the instantaneous rotational center point SP when the rear wheels are applied with the thrust and drag forces F2 as well as the side force F1.
That is, in FIG. 4 B, in the CTBA according to another example, in a double impact environment in which the rear wheels are simultaneously applied with thrust and drag forces, such as when the vehicle brakes or passes over a speed bump, rotation of the CTBA is offset by symmetrical rotation of the rear wheels, thereby guaranteeing the driving stability.
However, in FIG. 4 C, in a single impact environment in which one of the rear wheels is asymmetrically applied with thrust and drag forces F2, the corresponding rear wheel is induced to toe-out which makes the movement characteristics of the CTBA unstable in general, thereby deteriorating the driving stability as in the previous example according to the related art.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.